With the rapid development of the technologies of control, communication, computers, networks and the like, the information integration technology of an enterprise is rapidly developed from the factory site control to the product storage and transportation process. An industrial network plays an increasingly vital role in the fields of increasing the production speed, managing the production process, performing reasonable and efficient processing and the like. In recent years, the Ethernet enters the field of industrial control, and a great number of Ethernet-based industrial control networks appear. Meanwhile, with the development of the wireless technology, wireless-based industrial control networks gradually rise.
The WiFi technology is widely applied due to the advantages of low cost, rapid deployment and the like, and a research on WiFi-based industrial control networks is also conducted. For the handover problem caused by movement of terminal nodes, the 802.11 standard does not make clear specifications, so each WiFi equipment manufacturer deals with the problem independently. Although the latest 802.11r standard refines the technical specification for handover among APs, the standard only describes the handover process of a mobile terminal node (MN) from disconnection from an original AP to access into a new AP. Since the WiFi coverage range is limited, a terminal user frequently conducts the handover from one AP to another AP in the field of mobile application environment. Therefore, how to realize rapid and autonomous handover among APs becomes critical in the further development and application of WiFi.
When a data packet is transmitted in a network, the switch which forms a basic architecture of a wired network needs time to learn the location of each MAC address and then determines the switching path of data. Under an application scenario of rapid movement, the mobile terminal needs to continuously conduct rapid handover among a plurality of WiFi nodes in the process of transmitting and receiving the data. When WiFi network connection of the mobile terminal is hopped, a data flow to the mobile terminal still points to a wrong destination address. Such a condition continues until the switch learns a new location of the mobile terminal, which leads to sustained interruption of the data flow of the terminal user. To ensure that the mobile terminal conducts the handover among the WiFi nodes in time, a system needs to conduct sustained scan. When the speed is increased, the handover time will become a major problem. A research result indicates that the handover delay among APs is at least above hundreds of ms; moreover, at least 90% of delay is derived from a scanning stage, and the time consumed for certification and association is less than 10%. To this end, the scanning delay shall be reduced as far as possible so as to realize rapid AP handover.
As the research on the WiFi mobile applications constantly goes deeper, autonomous handover among the APs attracts more and more attention. However, the research finds that WiFi cannot realize rapid and autonomous handover among the APs.